1. Field of the Invention
The present invention relates to a resist coating method for forming a resist film over a wafer during manufacturing of a semiconductor device, and a resist coating apparatus using said method.
2. Description of the Background Arts
FIG. 11 is a schematic diagram illustrating a configuration of a conventional resist coating apparatus.
The resist coating apparatus 10 shown in FIG. 11 comprises a resist nozzle 2 for dripping resist 6 on the surface of wafer 1, a drive device for moving the resist nozzle 2 as desired above wafer 1, a resist supplier 4 consisting of, for instance, a pump for supplying the resist 6 from a resist storage portion 7 to the resist nozzle 2, a wafer support 8 upon which wafer 1 is held, and a wafer rotating device 5 consisting of, for instance, a motor for rotating the wafer support 8.
The drive device comprises a motor 3 and a belt and such like for rotating a rotatable support spindle of the resist nozzle 2 in accordance with the rotations of the motor. The resist solution supplied here is a solution in which the main component thereof has been adjusted to a suitable density using a solvent (thinner).
The conventional resist coating process will next be explained based on the flowchart shown in FIG. 12 and partial cross-sectional views of FIGS. 13A-13D showing a wafer support with a wafer on the top thereof in various steps.
Firstly, wafer 1, the underside of which has been adsorbed under vacuum, is positioned upon wafer support 8 and resist 6 is dripped from resist nozzle 2 onto wafer 1 approximately in the center thereof at an amount per unit of time of, for instance, 1 cc/sec for 3-4 seconds (Step S11 in FIG. 12; FIG. 13A)
Two types of dripping method are conventionally known: one is a static coating method in which, after the resist 6 has been dripped onto wafer 1, wafer 1 is rotated for a period of 20-25 seconds; and the other is a dynamic coating method in which wafer 1 is rotated for 20-25 seconds while the resist is being dripped. In these methods, a film of resist 6 evenly spreads over the surface of the wafer 1 (Step S12 in FIG. 12; FIG. 13B). The number of these rotations is determined in accordance with the thickness of the resist film. In this step, excess resist is removed by being scattered from the edges of the wafer 1.
Next, the resist 6 on the perimeter of the wafer 1 is removed and the underside of the wafer 1 is cleaned (Step S13 in FIG. 12; FIG. 13C).
Finally, the wafer 1 is rotated once more at high speed and the resist is dried (Step S14 in FIG. 12; FIG. 13D) to form a resist film as desired.
Such conventional methods have the disadvantage that the total amount of resist which needs to be dripped is considerably greater than the amount of resist which is actually left on top of the wafer. For instance, even when the rotation time and the number of rotations in each step are altered, at least 5 cc of resist must be dripped in order to form a resist film with thickness of 2000 nm on an unpatterned wafer with a diameter of 6 inches. Moreover, a patterned wafer with the same diameter would require at least 1 cc of resist to be dripped.